Method for producing microcapsule

ABSTRACT

A microcapsule produced by preparing a water-in-oil emulsion comprising an inner aqueous layer containing said water-soluble drug and a drug retaining substance therefor and an oil layer containing a polymer substance, then thickening or solidifying said inner aqueous layer to a viscosity of not lower than about 5000 centiposes and finally subjecting the resulting emulsion to in water drying gives prolonged release of water-soluble drug.

This application is a divisional of application Ser. No. 08/228,452,filed Apr. 15, 1994, U.S. Pat. 5,476,663 which is a continuation of Ser.No. 07/748,423 filed Aug. 22, 1991, now abandoned, which is a divisionalof Ser. No. 07/469,784 filed Jan. 24, 1990, now U.S. Pat. No. 5,061,492,which is a divisional of Ser. No. 07/103,117 filed Sep. 30, 1987, nowU.S. Pat. No. 4,917,893, which is a divisional of Ser. No. 06/940,614filed Dec. 11, 1986, now U.S. Pat. No. 4,711,782, which is a divisionalof Ser. No. 06/667,096 filed Nov. 1, 1984, now U.S. Pat. No. 4,652,441.

This invention relates to a prolonged release micro-capsule ofwater-soluble drug, and a method for producing the same.

A variety of dosage forms have been proposed for drugs which requirelong-term of repeated administration. As one of such dosage forms,European patent application publication No. 52,510 discloses amicrocapsule prepared by the phase separation technique using acoacervating agent such as mineral oils and vegetable oils. However,microcapsules prepared by this and other analogous processes have thedisadvantage that there tends to occur an inter-adhesion of particles inthe course of production.

Under the circumstances, the present inventors conducted studies todevelop a prolonged release preparation of water-soluble drug and foundthat a microcapsule having excellent properties can be produced withgood efficiency by interposing a Step of thickening or solidifying theinner aqueous layer of water in oil emulsion in the course ofmicroencapsulation by in water drying process. The above finding wasfollowed by further studies, which have resulted in the presentinvention.

The prolonged release microcapsule of the present invention is made bypreparing a water-in-oil emulsion comprising an inner aqueous layercontaining said water-soluble drug and a drug retaining substancetherefor and an oil layer containing a polymer substance (microcapsulewall substance) then thickening or solidifying said inner aqueous layerto a viscosity of not lower than about 5000 centipoises and finallysubjecting the resulting emulsion to in water drying process.

The water-soluble drug employed in the practice of this invention is adrug which is highly hydrophilic and has a low oil/water partitionratio. The term "low oil/water partition" ratio means that theoctanol/water partition ratio, for instance, is not greater than about0.1.

There is no particular limitation on the kind and type of saidwater-soluble drug. Thus, for example, biologically active polypeptidesand other antibiotics, antitumor agents, antipyretics, analgesics,antiinflammatory agents, antitussives and expectorants, sedatives,muscle relaxants, antiepileptics, antiulcer agents, anti-depressants,antiallergic drugs, cardiotonics, anti-arrhythmic agents, vasodilators,antihypertensive diuretics, antidiabetics, anticoagulants, haemostatics,antituberculotics, hormone drugs, antinarcotics, etc. may be mentionedas the water-soluble drug.

The biologically active polypeptides which are employed in accordancewith this invention are preferably those consisting of two or more aminoacid units and having a molecular weight between about 200 and about80000.

Examples of such polypeptides include luteinizing hormone releasinghormone (LH-RH) and its derivatives having LH-Pa like activity, i.e. thepolypeptides of the formula (I):

    (Pyr)Glu-R.sub.1 -Trp-Ser-R.sub.2 -R.sub.3 -R.sub.4 -Arg-Pro-R.sub.5(I)

[wherein R₁ is His, Tyr, Trp or p-NH₂ -Phe; R₂ is Tyr or Phe; R₃ is Glyor a D-amino acid residue; R₄ is Leu, Ile or Nle; R₅ is Gly-NH-R₆ (R₆ isH or a lower alkyl group which may optionally be substituted by OH) orNH-R₆ (R₆ is as defined above) or salts thereof] [see U.S. Pat. Nos.3,853,837, 4,008,209 and 3,972,859, British Pat. No. 1,423,083,Proceedings of the National Academy of Sciences of the U.S. of America78, 6509-6512 (1981)].

Referring to the above formula (I), the D-amino acid residue designatedby R₃ may be an α-D-amino acid residue of up to 9 carbon atoms (e.g.D-Leu, Ile, Nle, Val, Nval, Abu, Phe, Phg, Ser, Thr, Met, Ala, Trp,α-Aibu), and these may have suitable protective groups (e.g. t-butyl,t-butoxy, t-butoxycarbonyl, naphthyl). Of course, acid salts and metalcomplex compounds of peptides (I) can also be used in the same manner asthe aforementioned peptides (I).

In this specification, when amino acids, peptides, protective groups,etc. are mentioned, in connection with polypeptides (I), byabbreviations, such abbreviations are those established by IUPAC-IUBCommission on Biochemical Nomenclature or those used commonly in theparticular field of art and when there may exist optical isomers of suchamino acids, L-forms are intended unless otherwise indicated.

It should be understood that acetate of the polypeptide of formula (I)wherein R₁ =His, R₂ =Tyr, R₃ =D-Leu, R₄ =Leu, and R₅ =NHCH₂ --CH₃ isreferred to as TAP-144 in experimental and working examples.

As examples of such polypeptides, LH-RH antagonists (U.S. Pat. Nos.4,086,219, 4,124,577, 4,253,977, 4,317,815, 329,526, and 368,702) may bementioned.

As further examples of said polypeptides may be mentioned insulin,somatostatin, somatostatin derivatives (U.S. Pat. No. 4,087,390, U.S.Pat. No. 4,093,574, U.S. Pat. No. 4,100,117 and U.S. Pat. No.4,253,998), growth hormones, prolactin, adrenocorticotropic hormone(ACTH), melanocyte stimulating hormone (MSH), thyroid hormone releasinghormone (TRH), its salts, and derivatives thereof (U.S. Pat. No.3,957,247 and U.S. Pat. No. 4,100,152), thyroid stimulating hormone(TSH), luteinizing hormone (LH), follicle stimulating hormone (FSH),vasopressin, vasopressin derivatives [desmopressin [FoliaEndocrinologica Japonica 54, No. 5, p. 676-691 (1978)]], oxytocin,calcitonin, parathyroid hormone, glucagon, gastrin, secretin,pancreozymin, cholecystokinin, angiotensin, human placental lactogen,human cholionic gonadotropin (HCG), enkephalin, enkephalin derivatives[U.S. Pat. No. 4,277,394, European Patent Application Publication No.31567], endorphin, kyotorphin, interferons (αβγ), interleukins (I, II,and III), taftsin, thymopoietin, thymosin, thymostimulin, thymic humoralfactor (THF), serum thymic factor (FTS), and its derivatives (U.S. Pat.No. 4,229,438) and other thymic factors [Medicine in Progress 125, No.10, p. 835-843 (1983)], tumor necrosis factor (TNF), colony stimulatingfactor (CSF), motilin, dinorphin, bombesin, neurotensin, cerulein,bradykinin, urokinase, asparaginase, kallikrein, substance P analogueand antagonist, nerve growth factor, blood coagulation factors VIII andIX, lysozyme chloride, polymixin B, colistin, gramicidin, bacitracin,protein synthesis stimulating peptides (British patent No. 8232082),gastric inhibitory polypeptide (GIP), vasoactive intestinal polypeptide(VIP), platelet-derived growth factor (PDGF), growth hormone releasingfactor (GRF, somatocrinin), bone morphogenetic protein (BMP), epidemalegrowth factor (EGF), etc.

As examples of said antitumor agents, may be mentioned bleomycinhydrochloride, methotrexate, actinomycin D, mitomycin C, vinblastinesulfate, vincristine sulfate, daunorubicin hydrochloride, adriamycin,neocarcinostatin, cytosine arabinoside, fluorouracil,tetrahydrofuryl-5-fluorouracil, krestin, picibanil, lentinan,levamisole, bestatin, azimexon, glycyrrhizin, poly I:C, poly A:U andpoly ICLC.

As examples of said antibiotics, may be mentioned gentamicin, dibekacin,kanendomycin, lividomycin, tobramycin, amikacin, fradiomycin, sisomicin,tetracycline hydrochloride, oxytetracycline hydrochloride,rolitetracycline, doxycycline hydrochloride, ampicillin, piperacillin,ticarcillin, cephalothin, cephaloridine, cefotiam, cefsulodin,cefmenoxime, cefmetazole, cefazolin, cefotaxime, cefoperazone,ceftizoxime, moxolactam, latamoxef, thienamycin, sulfazecin, andazthreonam.

The aforementioned antipyretic, analgesic and antiinflammatory drugsinclude, for instance, sodium salicylate, sulpyrine, sodium flufenamate,sodium diclofenac, sodium indomethacin, morphine hydrochloride,pethidine hydrochloride, levorphanol tartrate and oxymcrphone. Asexamples of said antitussives and expectorants may be mentionedephedrine hydrochloride, methylephedrine hydrochloride, noscapinehydrochloride, codeine phosphate, dihydrocodeine phosphate, alloclamidehydrochloride, chlophedianol hydrochloride, picoperidaminehydrochloride, cloperastine, protokylol hydrochloride, isoproterenolhydrochloride, salbutamol sulfate and terbutaline sulfate. Examples ofsaid sedatives include chlorpromazine hydrochloride, prochlorperazine,trifluoperazine, atropine sulfate and scopolamine methylbromide. Themuscle relaxants include, among others, pridinot methanesulfonate,tubocurarine chloride and pancuronium bromide. The antiepilepticsinclude, for instance, sodium phenytoin, ethosuximide, sodiumacetazolamide and chiordiazepoxide hydrochloride. Examples of saidantiulcer drugs include metoclopramide and L-histidinemonohydrochloride. Examples of said antidepressants include imipramine,clomipramine, noxiptiline and phenelzine sulfate. The antiallergic drugsinclude, among others, diphenhydramine hydrochloride, chlorpheniraminemaleate, tripelenamine hydrochloride, methdilazine hydrochloride,clemizole hydrochloride, diphenylpyraline hydrochloride andmethoxyphenamine hydrochloride. The cardiotonics include, among others,trans-π-oxocamphor, theophyllol, aminophylline and etilefrinehydrochloride. The antiarrythmic agents include, for instance,propranolol hydrochloride, alprenolol hydrochloride, bufetololhydrochloride and oxyprenolol hydrochloride. The vasodilators include,among others, oxyfedrine hydrochloride, diltiazem hydrochloride,tolazoline hydrochloride, hexobendine and bamethan sulfate. Theantihypertensive diuretics include, among others, hexamethonium bromide,pentolinium, mecamylamine hydrochloride, ecarazine hydrochloride andclonidine hydrochloride. Examples of said antidiabetics include sodiumglymidine, glypizide, phenformin hydrochloride, buformin hydrochlorideand metformin. The anticoagulants include, among others, sodium heparinand sodium citrate. The haemostatic agents include, among others,thromboplastin, thrombin, menadione sodium bisulfite, acetomenaphthone,ε-amino-caproic acid, tranexamic acid, carbazochrome sodium sulfonateand adrenochrome monoaminoguanidine methanesulfonate. Among saidantituberculotics are isoniazid, ethambutol and sodiump-aminosalicylate. The hormone drugs are exemplified by prednisolonesuccinate, prednisolone sodium phosphate, dexamethasone sodium sulfate,betamethasone sodium phosphate, hexestrol phosphate, hexestrol acetateand methimazole. The antinarcotic agents include, among others,levallorphan tartrate, nalorphine hydrochloride and naloxonehydrochloride.

The proportion of said water-soluble drug depends on the kind of drug,expected pharmacological effect and its duration etc. but itsconcentration in the inner aqueous layer is selected from the range ofabout 0.001% to about 90% (w/w) and preferably 0.01% to 80% (w/w).

The drug retaining substance employed in accordance with this inventionis either a substance which is soluble in water and hardly soluble inthe organic solvent contained in said oil layer and when dissolved inwater assumes a viscous semi-solid consistency or a substance whichgains considerably in viscosity to provide a semi-solid or solid matrixunder the influence of an external factor such as temperature pH, metalions (e.g. Cu⁺⁺, Al⁺⁺⁺, Zn⁺⁺, etc.), organic acids (e.g. tartaric acid,citric acid, tannic acid, etc.), a salt thereof (e.g. calcium citrate,etc.), chemical condensing agents (e.g. glutaraldehyde, acetoaldehyde),etc.

As examples of such drug retaining substance may be mentioned natural orsynthetic mucilages and high molecular weight compounds.

Among such natural mucilages are gum acacia, Irish moss, gum karaya, gumtragacanth, gum guaiac, gum xanthane, locust bean gum, etc., whilenatural high molecular weight compounds include, among others, variousproteins such as casein, gelatin, collagen, albumin (e.g. human serumalbumin), globulin, fibrin, etc. and various carbohydrates such ascellulose, dextrin, pectin, starch, agar, mannan, etc. These substancesmay be used as they are or in chemically modified forms, e.g. esterifiedor etherified forms (e.g. methylcellulose, ethylcellulose,carboxymethylcellulose, gelatin succinate, etc.), hydolyzed forms (e.g.sodium alginate, sodium pectinate, etc.) or salts thereof.

As examples of said synthetic high molecular weight compounds may bementioned polyvinyl compounds (e.g. polyvinyl pyrrolidone, polyvinylalcohol, polyvinyl methyl ether, polyvinyl ether, etc.), polycarboxylicacids (e.g. polyacrylic acid, polymethacrylic acid, Carbopol [Goodrich &Co., U.S.A.], etc.), polyethylene compounds (e.g. polyethylene glycol,etc.) and polysaccharides (e.g. polysucrose, polyglucose, polylactose,etc.) and salts thereof.

Also included are those compounds which undergo condensation orcross-linking under the influence of said external factors to givemolecular weight compounds.

Among the aforementioned compounds, gelatin, albumin, pectin and agarare particularly desirable.

These compounds may be used alone or in combination and while theproportion of such compounds depends on the kind of compound, it isselected from the range of about 0.05% to 80% (w/w) in terms ofconcentration in the inner aqueous layer, preferably from the range ofabout 0.1% to 50% (w/w) on the same basis. It should, however, beunderstood that such compounds must be used in sufficient amounts toensure that the initial viscosity of the inner aqueous layer in thewater-in-oil emulsion described here-inafter will be not lower thanabout 5000 centipoises (cps), preferably not lower than about 10000 cps,or the inner aqueous layer may be increased in viscosity to not lowerthan about 5000 cps, preferably not lower than about 10000 cps, or besolidified by external factors.

The aforementioned polymer substance employed in the oil layer arepolymers hardly soluble or insoluble in water and biocompatible. Asexamples of such polymer substance may be mentioned biodegradablealiphatic polymers (e.g. polylactic acid, polyglycolic acid, polycitricacid, polymalic acid, etc.), poly-α-cyanoacrylic acid esters,poly-β-hydroxybutyric acid, polyalkylene oxalate (e.g. polytrimethyleneoxalate, polytetramethylene oxalate, etc.), poly(ortho-esters),poly(ortho-carbonate), other polycarbonate (e.g. polyethylene carbonate,polyethylene propylene carbonate, etc.), polyamino acids (e.g.poly-γ-benzyl-L-glutamic acid, poly-L-alanine, poly-γ-methyl-L-glutamicacid, etc.) and so on. As further examples of biocompatible polymersubstance may be mentioned, polystyrene, polyacrylic acid,polymethacrylic acid, copolymer of acrylic acid and methacrylic acid,nylon, tetron, polyamino acid, silicone polymer, dextran stearate,ethylcellulose, acetylcellulose, nitrocellulose, polyurethane, maleicanhydride copolymers, ethylene-vinyl acetate copolymer, polyvinylacetate, polyvinyl alcohol, polyacrylamide, etc. These polymersubstances may be used alone or in the form of copolymers or mixtures oftwo or more species or of salts.

When used in injectable preparations, biodegradable polymers, among saidpolymers substances, are especially desirable, and as preferableexamples of such polymer substance maybe mentioned polylactic acid and acopolymer of lactic acid and glycolic acid and these mixtures.

The average molecular weight of such a polymer substance as used inaccordance with this invention preferably ranges from about 2000 toabout 800000 and is more desirably 5 selected from the range of about5000 to about 200000.

When a lactic acid-glycolic acid copolymer is used as said polymer, itscomonomer ratio is preferably in the range of about 100/0 through about50/50.

The proportion of such a polymer substance depends on the strength ofpharmacological activity of the water-soluble drug used and the rate andduration of release of the drug. By way of illustration, the proportionof this polymer substance may range from 1/5 to 10000 times andpreferably 1 to 1000 times the weight of the water-soluble drug.

The concentration of said polymer substance in the oil layer is about0.5 to 90% (w/w) and preferably about 2 to 60% (w/w).

The solution containing said polymer substance (oil layer) is a solutionof the polymer substance in a solvent. The solvent for this purposeshould be one which boils at a temperature up to about 120° C. and isimmiscible with water and capable of dissolving the polymer substanceand as such there may be mentioned halogenated alkanes (e.g.di-chloromethane, chloroform, chloroethane, dichloroethane,trichloroethane, carbon tetrachloride, etc.), ethyl acetate, ethylether, cyclohexane, benzene, n-hexane and toluene. These solvents may beused alone or in combination.

With regard to the microencapsulation procedure, the drug retainingsubstance in an amount sufficient to give the aforementionedconcentration is first dissolved in water and, then, the water-solubledrug is added in an amount sufficient to give the aforementionedconcentration, whereby an inner aqueous layer is provided.

As a pH-adjusting agent for maintaining the stability and solubility ofthe water-soluble drug, there may be incorporated in this inner aqueouslayer such an additive as carbonic acid, acetic acid, oxalic acid,citric acid, tartaric acid, succinic acid or phosphoric acid, sodium orpotassium salts thereof, hydrochloric acid or sodium hydroxide.Moreover, as a stabilizer for the water-soluble drug, there may also beadded such an agent as albumin, gelatin, citric acid, ethylenediaminesodium tetraacetate, dextrin, sodium hydrosulfite, etc. The inneraqueous layer may also contain a preservative such as p-oxybenzoic acidesters (e.g. methylparaben, propylparaben, etc.), benzyl alcohol,chlorobutanol, thimerosal, etc.

The inner aqueous layer thus prepared is poured into a solution of saidpolymer substance (oil layer) and the mixture is emulsified to give awater-in-oil emlusion.

The emulsification can be effected by the conventional dispersiontechniques. For example, intermittent shaking, mixing by means of apropeller mixer, turbine mixer or the like, colloid mill operation,mechanical homogenization, ultrasonication, etc. may be utilized.

When the viscosity of the inner aqueous layer in such a water-in-oilemulsion is more than about 5000 centipoises or preferably over about10000 centipoises from the beginning, the emulsion is immediatelysubjected to a desorption procedure but, otherwise, resort is had to anexternal factor to thicken the inner aqueous layer to a viscosity overabout 5000 centipoises or preferably over about 10000 centipoises orsolidify the same.

Exemplary procedures for increasing the viscosity include a heattreatment, cooling to a low temperature, freezing, rendering the pHacidic or alkaline, or adding such an agent as metal ions (e.g. iron ionfor gum acacia, copper ion for carboxymethylcellulose, or calcium ormagnesium ion for sodium pectinate) or organic acids or salts thereof(e.g. calcium citrate for sodium alginate, or adipic acid or tartaricacid for polyvinyl alcohol). There may also be mentioned the techniqueof cross-linking and condensing the polymer substance in the inneraqueous layer using a chemical condensing agent (e.g. glutaraldehyde,acetaldehyde, etc.)

With regard to the heat treatment, the procedure must be carried out ina closed vessel so as to avoid evaporation of the solvent contained inthe oil layer. The temperature is virtually optional only if it ishigher than the gelation temperature. Taking proteins as an example, thetemperature is generally about 40° to 120° C. and the time is about 5minutes to about 8 hours. This treatment thickens or solidifies theinner aqueous layer.

The technique of cooling the emulsion to a low temperature comprisescooling it to about -5° C. to about 35° C. and maintaining the lowtemperature with stirring for about 1 minute to 6 hours. In the case ofagar whose gelation point is about 40° C., the emulsification isconducted under heating at about 50° to 80° C. and, then, caused to gelat the above-mentioned temperature. For all types of inner aqueouslayer, it may be frozen by cooling at about -60° C. to 0° C. but thetemperature should not be below the solidification point of the oillayer.

As regards the procedure of adding a metal ion, an organic acid or asalt thereof, the amount thereof depends on the amount of the drugretaining substance in the inner aqueous layer and may range from about1/4 to 20 molar equivalents and preferably from about 1 to 10 molarequivalents. The time required for said thickening or solidification ispreferably not more than about 6 hours.

With regard to the technique of cross-linking and condensing the highmolecular compound in the inner aqueous layer with chemical condensingagent, such condensing agent may for example be an aqueous solution ofglutaraldehyde or acetaldehyde or a solution of the same in an organicsolvent such as halogenated alkanes (e.g. chloroform, dichloromethane,etc.), toluene, etc. Particularly, a solution in the latter solventwhich is miscible with the solvent used in the oil layer is desirable,because the particle size of the inner aqueous layer is not increased.The chemical condensing agent is added in a proportion of about 2 to 5molar equivalents based on the drug retaining substance in the inneraqueous layer and the mixture is reacted under stirring for about 1 to10 hours.

More specifically, taking gelatin as an example of said drug retainingsubstance, a water-in-oil emulsion of predetermined particle size isfirst prepared and then cooled to about 0° to 10° C. for about 5 to 30minutes with constant stirring, whereby the inner aqueous layer iscaused to gel into semi-solid consistency. When agar is used as the drugretaining substance, the desired semi-solid consistency can be obtainedby using a somewhat lower concentration than in the case of gelatin andthe same procedure as that for gelatin. When albumin is employed,solidification is effected with a condensing agent such asglutaraldehyde. In this case, the water-soluble drug is dissolved in aca. 5 to 50% aqueous solution of human serum albumin and the resultingsolution is added to the organic solvent solution of high polymer toprepare a water-in-oil emulsion. Thereto is added a ca. 1 to 50%solution of glutaraldehyde in an organic solvent miscible with the oillayer and the mixture is reacted under stirring for about 1 to 10 hoursso as to solidify the inner aqueous layer. In this procedure, albuminmay be replaced with other substances that can be thickened orsolidified by cross-linking and condensation, such as globulin, gelatin,casein, collagen and other polyamino acids. After the reaction, acompound which is ready to react with the condensing agent, e.g. anamino compound such as ethanolamine, aminoacetic acid, etc., may beadded so as to inactivate the residual condensing agent.

When a substance capable of increasing in viscosity on alteration of pH,such as carboxyvinyl polymer (Carbopol, B. F. Goodrich, U.S.A.) is addedto the inner aqueous layer, a ca. 1 to 20% solution of sodium hydroxidein ethanol or methanol is separately prepared and a small quantity ofthe solution is added to the water-in-oil emulsion to increase theviscosity of the inner aqueous layer.

the water-in-oil emulsion thus prepared is subjected to in water drying.Thus, this water-in-oil emulsion is added to a third aqueous layer togive a W/O/W ternary layer emulsion and, finally, the solvent in the oillayer is desorbed to give microcapsules.

An emulsifying agent may be added to the third or outer aqueous layer.It may be virtually any emulsifier that forms a stable oil-in-wateremulsion, and is thus exemplified by anionic surfactants (e.g. sodiumoleate, sodium stearate, sodium laurylsulfate, etc.), nonionicsurfactants(e.g. polyoxyethylene sorbitan fatty acid esters [Tween 80and Tween 60, Atlas Powder, U.S.A.], polyoxyethylene castor oilderivatives [HCO-60 and HCO-50, Nikko Chemicals, Japan], etc.),polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl-cellulose,lecithin, gelatin, etc. Such emulsifiers may be used either alone or incombination. The concentration of the emulsifier may be selected fromthe range of about 0.01% to 20% and is prefearbly in the range of about0.05% to 10%.

The aforesaid desorption of the solvent from the oil layer can beaccomplished by the conventional technique. Thus, such desorption iseffected by gradual decrease of pressure under agitation with apropeller mixer or magnetic stirrer or by adjusting the degree of vacuumin a rotary evaporator. When the higher the stirring speed is, thesmaller the diameter of the product microcapsule is. The time requiredfor such procedures can be shortened by warming the W/O/W emulsion bydegrees so as to make the solvent desorption thorough, after thesolidification of the polymer has progressed to some extent and the lossof the drug from the inner aqueous layer has decreased. When thethickening or solidification is effected by techniques other thantemperature control, the desorption may be effected by allowing theW/O/W emulsion to stand under stirring, warming the emulsion or blastingit with nitrogen gas. The process of desorption of the solvent is animportant process having great bearings on the surface structure ofmicrocapsules which governs the release of the drug. For example, whenthe desorption speed is increased, pits in the surface layer increase innumber and size so that the release rate of the drug is increased.

The microcapsules obtained in the above manner are recovered bycentrifugation or filtration, and the free water-soluble drug,emulsifying agents, etc. on the surface are removed by repeated washingwith water, then, if necessary, the microcapsules are warmed underreduced pressure to achieve a complete removal of moisture and of thesolvent from the microcapsule wall.

The above microcapsules are gently crushed and sieved, if necessary, toremove coarse microcapsules. The particle size of microcapsules dependson the desired degree of prolonged release. When they are to be used asa suspension, its size may be within the range satisfying the requireddispersibility and needle pass requirements. For example, the averagediameter may range from about 0.5 to 400 μm and preferably from about 2to 200 μm.

The method of this invention enables one to apply a high shear stress inthe preparation of the W/O/W emulsion with a less breakdown of the inneraqueous layer and facilitates particle size control to thereby providefine microcapsules with good efficiency. The additional commercialadvantage of this invention is that the required quantity of organicsolvent is as small as compared with the drying-in-oil technique.

Moreover, the microcapsules produced by the method of this inventionfeature a reduced coalescence of individual microcapsules duringproduction so that they are more truly spherical in configuration. Inaddition, desorption of the solvent from the oil layer can be easilycontrolled to adjust the surface structure (for example, the number andsize of fine holes which serve as main routes of the drug release) ofmicrocapsules.

The microcapsules according to this invention can be administered inclinical practice directly as fine granulets or as formulatedpreparation into a variety of preparations. Thus, they can be used asraw materials for the production of final pharmaceutical preparations.

Such preparations include, among others, injections, oral preparations(e.g. powders, granules, capsules, tablets, etc.), nasal preparations,suppositories (e.g. rectal, vaginal), and so on.

When the microcapsules according to this invention are to be processedinto an injectable preparation, they are dispersed in an aqueous vehicletogether with a dispersing agent (e.g. Tween 80, HCO-60 (NikkoChemicals), carboxymethylcellulose, sodium alginate, etc.), preservative(e.g. methyl-paraben, propyl-paraben, benzyl alcohol, chlorobutanol,etc.), isotonizing agent (e.g. sodium chloride, glycerin, sorbitol,glucose, etc.), etc. The vehicle may also be a vegetable oil (e.g. oliveoil, sesame oil, peanut oil, cottonseed oil, corn oil, etc.), propyleneglycol or the like. In this manner, a prolonged release injection can beproduced.

The prolonged release injection made from said microcapsules may befurther supplemented with an excipient (e.g. mannitol, sorbitol,lactose, glucose, etc.), redispersed, and then be solidified byfreeze-drying or spray-drying, and on extemporaneous addition of adistilled water for injection or suitable vehicle for the 35reconstitution, such preparation gives a prolonged release injectionwith greater stability.

When the microcapsules according to this invention are to be processedinto tablets, they are mixed with an excipient (e.g. lactose, sucrose,starch, etc.), disintegrating agent (e.g. starch, calcium carbonate,etc.), binder (e.g. starch, gum arabic, carboxymethylcellulose,polyvinylpyrrolidone, hydroxypropylcellulose, etc.) or/and lubricant(e.g. talc, magnesium stearate, polyethylene glycol 6000, etc.), and themixtures are compressed in molds.

To manufacture a nasal preparation from the microcapsules according tothis invention, they are provided solid, semi-solid or liquid state inthe conventional manner. To manufacture the solid nasal preparation forinstance, the microcapsules either as they are or together with anexcipient (e.g. glucose, mannitol, starch, microcrystalline cellulose,etc.) and/or thickener (e.g. natural mucilages, cellulose derivatives,polyacrylates, etc.) are processed into a powdery composition. To make aliquid composition, the microcapsules are processed into an oily oraqueous suspension in substantially the same manner as in the case ofinjections. The semi-solid preparation may be an aqueous or oily gel orointment. In any case, there may be added a pH adjusting agent (e.g.carbonic acid, phosphoric acid, citric acid, hydrochloric acid, sodiumhydroxide, etc.), a preservative (e.g. p-hydroxybenzoic acid esters,chlorobutanol, benzalkonium chloride, etc.), etc.

A suppository of the microcapsules according to this invention, whetherin oily or aqueous solid or semi-solid state or in liquid state, can beproduced in the per se conventional manner. The kind of oleagenous basefor such composition is optional only if it will not dissolve themicrocapsules. Thus, for example, higher fatty acid glycerides [e.g.cacao butter, Witepsol (Dynamit-Novel, West Germany), etc.],intermediate fatty acids [e.g. Miglyol (Dynamit-Novel, etc.] andvegetable oils (e.g. sesame oil, soybean oil, cottonseed oil, etc.) maybe mentioned. The aqueous base is exemplified by polyethylene glycol andpropylene glycol, while the aqueous gel base may be selected from amongnatural mucilages, cellulose derivatives, vinyl polymers, polyacrylates,etc.

The dosage of the prolonged release preparation according to thisinvention depends on the kind and amount of the active ingredient (i.e.water-soluble drug), dosage form, duration of drug release, recipientanimal (e.g. warm-blooded animals such as mouse, rat, horse, cattle,man), and object of treatment. It is, however, sufficient to ensure thatthe effective dose of the active ingredient will be administered. Forexample, the amount per dose to humans may be selected from the range ofabout 1 mg to 10 g, preferably about 10 mg to 2 g, in terms of theweight of microcapsules.

When an injectable dosage form is employed, the volume of the suspensionmay be selected from the range of about 0.1 to 5 ml, preferably about0.5 to 3 ml.

In this manner, there are provided pharmaceutical compositions made upof a water-soluble drug, a drug retaining substance and a biocompatiblepolymer which are capable of continuous and prolonged release of thedrug.

The prolonged release preparation according to this invention has thefollowing and other advantages.

(1) The prolonged release of water-soluble drugs in various dosage formscan be ensured. Particularly when a long-term treatment with injectionsis required for the desired effect, the preparation helps achieve thedesired pharmacological effects with an administration schedule of oncea month or a week or even once a year, instead of giving injectionsevery day. Moreover, compared with the conventional sustained releasedrugs, the prolonged release preparation according to this inventionensures longer sustained effects.

(2) When injections are prepared using biodegradable polymers, surgicalprocedures such as implantation are not required but the preparationscan be administered subcutaneously or intramuscularly as easily asordinary injectable suspensions, not entailing the need for removal fromthe body.

The preparation according to this invention can be directly administeredto the tumor itself, the site of inflammation or the receptor region, sothat systemic side effects can be controlled and the drug be allowed toact on the target organ for a longer time period with efficiency, thusmaking for increased drug efficacy. Moreover, it can be used inintra-arterial administration in the vascular embolic therapy proposedby Kato et al for cancer of the kidney and of the lung (Lancet II,479-480, 1979).

(3) The release of the active ingredient is continuous, and in the caseof antihormones, receptor antagonists, etc., greater pharmacologicaleffects are obtained than by daily pulsatile administration.

(4) Since a drug retaining substance is employed, the water-soluble drugcan be incorporated in the microcapsule more easily and efficiently thanby the conventional drying-in-solvent technique. Moreover, themicrocapsules are fine and more truly spherical in configuration.

(5) By varying the rate of desorption of the solvent from the polymerconstituting the microcapsule wall, the number and size of fine holes inthe surface layer of each microcapsule which are determinant of the rateof drug release can be freely controlled.

The following experimental and working examples are further illustrativeof this invention.

EXPERIMENTAL EXAMPLE 1

The repeated administration of TAP-144 to mature female rats in massivedoses causes desensitization of the pituitary-gonad system to therebyhalt the sexual cycle in the diestrous stage. It is known that this haltof the sexual cycle is promptly recovered as the administration ofTAP-144 is discontinued. Therefore, using this halt of the sexual cycleof female rats as an indicator, the present inventors investigates thedurations of action of 7 different microcapsules prepared usingdifferent polymers, which are among the 8 kinds of microcapsulesaccording to Example 1 and of two other microcapsules (No. 039 and No.0310) which are produced by using TAP-144 for the inner aqueous layer inthe amounts of 1/2 and 2.5 times, respectively, but in otherwise thesame manner as Example 1. Thus, using SD female rats (aged 14 to 16weeks) which are confirmed to show a normal 4-day cycle by theexamination of vaginal smears during the preceding period of at least 1week in groups of 5 individuals, each of the above-mentionedmicrocapsules is injected subcutaneously at the back of the neck in adose of 3 mg/kg as TAP-144. Thereafter, the examination of vaginalsmears is carried out every day to monitor changes in sexual cycle. Themicrocapsules are administered either in the form of oily suspensions inpurified sesame oil or in the form of aqueous suspensions prepared usinga dispersed vehicle constituted with 0.2% Tween 80, 0.5% sodiumcarboxymethylcellulose, 0.14% methyl-paraben, 0.014% propyl-paraben and8% D-sorbitol in distilled water for injection.

The results are presented in Table 1. It will be apparent from Table 1that all of the microcapsules according to this invention have everysatisfactory durations of action.

                  TABLE 1                                                         ______________________________________                                                                 Duration of action.sup.a)                            Microcapsule No.                                                                            Formulation                                                                              (days)                                               ______________________________________                                        031           Aqueous    ≧105                                          033           Aqueous    19.0 ± 0.6                                        033           Oily       19.2 ± 0.5                                        034           Aqueous    ≧123                                          035           Aqueous    59.0 ± 7.6                                        036           Aqueous    117.2 ± 1.8                                       037           Aqueous    39.8 ± 1.8                                        038           Aqueous    35.0 ± 1.3                                        039           Aqueous    60.0 ± 6.2                                        0310          Aqueous    19.6 ± 0.4                                        ______________________________________                                         .sup.a) Mean ± standard error for 5 rats.                             

EXPERIMENTAL EXAMPLE 2

The repeated administration of TAP-144 to male rats in massive dosescauses an atrophy (decrease of organ weight) of the inner genital organsdue to desensitization of the pituitary-gonad system. Using this action,the duration of action of the TAP-144 microcapsules produced in Example1 are investigated. Thus, No. 032 and No. 035 microcapsules according toExample 1 are injected subcutaneously at the back of the neck of SD malerats (aged 6 weeks) in the dose of 900 μg as TAP-144 after 1, 2 and 4weeks the inner genital organs are removed and weighed. As control,untreated rats of the same age are used and the percentages of organweights relative to the control organ weights are calculated. Theresults are shown in Table 2. In the group of rats given No. 032microcapsules, no marked difference is found between oily and aqueousformulations and a marked weight decrease persisting for 4 weeks isnoted in the weight of testis. A marked weight decrease is also observedin the seminal vesicle, with a significant difference being noted evenat 2 weeks. In the No. 035 microcapsule group, too, marked weightdecreases of both the testis and seminal visicle are found after 1 week.The above results indicate that the TAP-144 prolonged release injectionsaccording to this invention have satisfactory durations of action.

                  TABLE 2                                                         ______________________________________                                                                  Microcapsule                                                  Microcapsule No. 032                                                                          No. 035                                             Time   Organ    Oily       Aqueous  Aqueous                                   ______________________________________                                        1 Week Testis   58.1 ± 8.3**                                                                          57.9 ± 7.4**                                                                        62.4 ± 5.3**.sup.a)                           Prostate 94.6 ± 4.7                                                                            92.9 ± 9.9                                                                          86.7 ± 7.9                                    Seminal  67.6 ± 10.6                                                                           62.7 ± 10.7*                                                                        66.4 ± 7.7*                                   vesicle                                                                2 Weeks                                                                              Testis   53.4 ± 6.5**                                                                          65.1 ± 10.6*                                           Prostate 67.2 ± 6.3**                                                                          85.1 ± 7.3                                             Seminal  39.5 ± 6.3**                                                                          56.2 ± 7.8*                                            vesicle                                                                3 Weeks                                                                              Testis   77.1 ± 5.7**                                                                          58.0 ± 5.7**                                           Prostate 97.4 ± 4.6                                                                            87.2 ± 5.9                                             Seminal  89.3 ± 2.7                                                                            80.5 ± 6.4*                                            vesicle                                                                ______________________________________                                         .sup.a) Percentages relative to the organ weights of control rats             (untreated, the same age)                                                     **A highly significant difference (P<0.01) from control by ttest.             *A significant difference (P<0.05) from control by ttest.                

EXAMPLE 1

In 2.5 ml of a 20% aqueous gelatin solution prepared by warming (at 60°to 70° C.) is dissolved 200 mg of TAP-144 and the whole solution isadded to 10 ml of a 20% dichloromethane solution of one of the 7different lactic acid or lactic acid-glycolic acid polymers (2 runs forpolylactic acid with a molecular weight of 50000). The mixture isultrasonicated (20 KHz, 100 W, a few minutes, the ultrasonicatormanufactured by Ohtake Seisakusho Inc., Japan) to give a microfine W/Oemulsion. This emulsion is immediately cooled with ice to cause gelationof the gelatin layer. This is then added to 100 ml of 0.5% polyvinylalcohol (Gosenol EG-40, the Nippon Synthetic Chemical Industry Co.,Ltd., Japan)-1/30 M 5 phosphate buffer (pH 6.0) and dispersed using ahomogenizer (T.K. Homomixer, Tokushu Kika Kogyo Inc., Japan, 30 V)(3,000r.p.m.) for 15 seconds to give a W/O/W emulsion. This emulsion isquickly transferred to a rotary evaporator in which the dichloromethaneis desorbed under ice-cooling. After foaming has subsided, the emulsionis warmed to 30° to 40° C. in a constant-temperature water bath forcomplete desorption of the organic solvent. The hardened microcapsulesare then filtered through a glass filter and washed 5 times with 10 mlportions of distilled water. It is then spread on a glass dish andallowed to dry under reduced pressure for 1 to 3 days. The product issieved through a 100-mesh screen (Sieve opening: 147 μm) to give TAP-144microcapsules.

In 10 ml of dichloromethane is dissolved 10 mg of the abovemicrocapsules and TAP-144 in the solution is extracted with 10 ml ofdistilled water under shaking for 10 minutes. The TAP-144 content of theaqueous layer is assayed by high performance liquid chromatography(HPLC) and the percentage of TAP-144 taken UP into the microcapsulesrelative to the initial amount of TAP-144 added is calculated. Theresults are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                 Polymer                                                                         Lactic acid/            Takeup                                     Microcapsule No.                                                                         glycolic acid                                                                             Mol. weight (%)                                        ______________________________________                                        Control                                                                              021     100/0       50000      6.7                                            022     100/0       50000      5.5                                            023     100/0       50000      1.9                                     This   031     100/0       73000     70.4                                     invention                                                                            032     100/0       50000     70.7                                            033     100/0       50000     71.5                                            034     100/0       15000     54.8                                            035     100/0        6800     55.8                                            036     88.7/11.3   19000     44.0                                            037     78.1/21.9   10000     58.3                                            038     54.5/45.4   20000     53.1                                     ______________________________________                                    

It will be apparent from Table 3 that when the in water drying techniqueunder the same conditions is carried out without gelation of the firstaqueous layer (control), the takeup ratio are as low as 1.9 to 6.7%whereas the takeup ratio for the microcapsules according to thisinvention are as high as 44.0 to 71.5%. In the repeated experiments bythe same production procedure using polylactic acid with a molecularweight of 50000, to take up ratio are almost comparable.

EXAMPLE 2

In a 20% aqueous gelatin solution prepared by warming (60° to 70° C.) isdissolved 200 mg of TAP-144. This solution is added when hot to a 20%dichloromethane solution of polylactic acid (average mol. wt. 50000) andthe mixture is ultrasonicated in the same manner as Example 1 to give afine W/O emulsion. Separately, 5 ml of a 25% aqueous solution ofglutaraldehyde is extracted with 5 ml of dichloromethane (using theaforementioned ultrasonicator, 50 W, 2 min.) and the organic layer isadded to the emulsion prepared above. Using a four-blade rotary mixer,the mixture is reacted at room temperature under agitation for 6 hours.Thereafter, 4 ml of ethanolamine is added and the reaction is furtherconducted for 1 hour. After ice-cooling, the reaction mixture is pouredin 100 ml of ice-cooled 0.5% polyvinyl alcohol-1/30 M phosphate buffer(pH 6.0).

Then, as in Example 1, a W/O/W emulsion is prepared and the organicsolvent is desorbed to give TAP-144 microcapsules (Microcapsule No.0311). In addition, a 30% aqueous solution of human serum albumin inlieu of said 20% gelatin is treated with glutaraldehyde in the samemanner as above to prepare TAP-144 microcapsules (Microcapsule No.0312).

These microcapsules are dispersed in purified sesame oil and thedispersions are subcutaneously injected into mature female rats at adose of 12 mg/kg as TAP-144 in the same manner as Experimental Example 1to assess the durations of action of the respective prolonged releasepreparations.

The results are presented in Table 4. It will be seen that their actionslast for about 4 months, indicating that these microcapsules aresatisfactory prolonged release preparations.

                  TABLE 4                                                         ______________________________________                                        Microcapsule               Duration of actions.sup.a)                         No.      Drug retaining substance                                                                        (days)                                             ______________________________________                                        0311     20% gelatin       ≧147                                        0312     30% human serum albumin                                                                         114.8 ± 5.9                                     ______________________________________                                         .sup.a) Mean ± standard error for 5 rats                              

EXAMPLE 3

In 10 ml of dichloromethane is dissolved 3 g of lactic acid-glycolicacid copolymer (monomer ratio: 88.7/11.3, average mol. wt. 19000)followed by addition of 3 ml of a 30% aqueous solution of gelatin(dissolved at 60° C.). Then, a solution of 200 mg of LH-RH antagonist(N-Ac-[D-P-Cl-Phe¹,2, D-Trp³,D-Arg⁶, D-Ala¹⁰ ]-LH-RH) (Europe PatentApplication Publication No. 81,877) is added and the mixture isultrasonicated in the same manner as Example 1 to give a W/O emulsion.This emulsion is immediately cooled with ice and dispersed in awater-cooled 0.5% aqueous solution of polyvinyl alcohol. Then, thedichloromethane is desorbed and LH-RH antagonist microcapsules recoveredin the same manner as Example 1.

EXAMPLE 4

In 2.5 ml of a 20% aqueous solution of gelatin (prepared at 60° C.) isdissolved 500 mg of an enkephalin derivative (H-Tyr-D-Met(O)-Gly-EtPhe-NH-NHCOCH₃. AcOH ) (U.S. Pat. No. 4,277,394; TAI-1399) andthe solution is added to 10 ml of a 20% solution of polylactic acid(average mol. wt. 50000) in dichloromethane. The mixture is furtherworked up in the same manner as Example 1 to give a W/O emulsion. Underice-cooling, this emulsion is further worked up in 0.5% polyvinylalcohol-1/30 M phosphate buffer (pH 6.0) to give a W/O/W emulsion. Theorganic solvent is then desorbed under reduced pressure in a rotaryevaporator and the mixture is warmed from ice-cooling to 35° C. and whenfoaming has subsided, it is sieved through a 100-mesh screen andfiltered through, a glass filter to give TAI-1399 microcapsules.

The microcapsules thus produced are washed 4 times with 10 ml portionsof distilled water and redispersed in a mixed aqueous solution of 0.2%Tween 80, 0.5% sodium carboxymethylcellulose and 10% mannitol, followedby freeze-drying to give a prolonged release preparation of TAI-1399which is of a reconstituted suspension type and the action of whichlasts in vivo for more than about 2 weeks.

EXAMPLE 5

In a 20% aqueous solution of gelatin (prepared at 60° C.) is dissolved2.2 billion units of γ-interferone and the solution is added to 10 ml ofa 20% dichloromethane solution of polylactic acid (average mol. wt.73000). Then, the same procedure as Example 1 is followed to give aW/O/W emulsion under ice-cooling, remove the solvent in a rotaryevaporator and recover solid microcapsules by filtration to giveγ-interferone microcapsules.

The above microcapsules are washed 4 times with 10 ml portions ofdistilled water and dispersed in 50 ml of a mixed aqueous solution of0.2% Tween 80, 0.5% sodium carboxymethylcellulose and 8% D-sorbitol, and1 ml portions of the dispersion are distributed into glass vials andfreeze-dried. The contents of each vial are extemporaneously redispersedin 1 ml of distilled water for injection containing 0.4% methyl-parabenand 0.04% propylparaben to give a prolonged release injection containingabout 25,000 thousand units of γ-interferone per dose.

EXAMPLE 6

In 2.5 ml of distilled water are dissolved 300 mg of synthetic serumthymic factor (FTS: H-Glu-Ala-Lys-Ser-Gln-Ala-Gly-Ser-Asn-OH) and 750 mgof human serum albumin, and the whole solution is added to 10 ml of adichloromethane solution containing 3 g of lactic acid-glycolic acidcopolymer (monomer ratio: 78.1/21.9, average mol. wt. 10000).Thereafter, the same procedure as Example 1 is followed to prepare a W/Oemulsion. To this emulsion is added 3 ml of a dichloromethane extract of25% aqueous glutaraldehyde (3 ml) and the reaction is carried out understirring for 5 hours. Then, 3 ml of ethanolamine is added and themixture is further stirred for 1 hour. This W/O emulsion is poured in100 ml of a 0.5% aqueous solution of polyvinyl alcohol and the solutionis worked up in the same manner as Example 1 to give a W/O/W emulsion.Finally, the solvent is removed in rotary evaporator and the productmicrocapsules are recovered.

The microcapsules thus obtained are dispered in 20 ml of the samedispersing medium as the one used in Example 5 and 2 ml portions of thedispersion are distributed into glass vials and freeze-dried to give aprolonged release injection containing about 15 mg of FTS per dose.

EXAMPLE 7

In 2.5 ml of a 2% aqueous solution of agar (liquefied by warming at 60°C.) is dissolved citrate of a thyroid hormone derivative (DN-1417) ofthe following formula: ##STR1## This solution is added to 10 ml of a 20%solution of polylactic acid (average mol. wt. 50000) in dichioromethane.The mixture is worked up in the same manner as Example 1 to give a W/Oemulsion which is further processed into a W/O/W emulsion under icecooling. Finally, the organic solvent is removed to give DN-1417microcapsules.

These microcapsules are recovered by filtration, dried in vacuo at 40°C. for 24 hours and sieved through a 100-mesh screen. The product (500mg) is filled into a vial to give a prolonged release injectioncontaining about 75 mg of DN-1417 which is used by a reconstitutedsuspension.

EXAMPLE 8

In 10 ml of dichloromethane is dissolved 2 g of lactic acid-glycolicacid copolymer (monomer ratio: 54.5/ 45.5, average mol. wt. 20000). Tothis solution is added 3 ml of a 20% aqueous gelatin solution containing400 mg of mitomycin C (liquified by warming at about 60° C.) and themixture is worked up in the same manner as Example r to give mitomycin Cmicrocapsules.

The microcapsules are dried in vacuo and sieved through a 100-meshscreen. A 200 mg of the product is taken as a prolonged releaseinjection containing about 20 mg of mitomycin C which is a reconstitutedsuspension for injection.

EXAMPLE 9

To a 20% dichloromethane solution of lactic acid/glycolic acid copolymer(monomer ratio: 78.1/21.9, average mol. wt. 10000) is added 3 ml of a20% aqueous gelatin solution containing 1.5 g of gentamycin sulfate(liquefied by warming). The mixture is further worked up in the samemanner as Example 1 to give microcapsules.

These microcapsules are dried in vacuo and sieved, and 350 mg of theproduct is taken as a prolonged release preparation containing about 100mg of gentamycin for use by a reconstituted suspension.

EXAMPLE 10

In 10 ml of dichloromethane is dissolved 3 g of polylactic-acid (averagemol. wt. 15000) followed by addition of 3 ml of a 20% aqueous gelatinsolution containing 43000 units of blood coagulation factor VIII and 15mg of sodium citrate. The mixture is worked up in the same manner asExample 4 to give microcapsules.

This product is dispersed in 20 ml of dispersing medium and 2 mlportions are filled into vials to freeze dry to give a prolonged releaseinjection for a reconstituted suspension containing about 3000 units ofblood coagulation factor VIII in each vial.

EXAMPLE 11

In 3 ml of a 20% aqueous gelatin solution (liquified by warming) isdissolved 2 g of sulpyrine and the solution is added to 10 ml of a 25%dichloromethane solution of lactic acid-glycolic acid copolymer(54.5/45.5, average mol. wt. 20000). Finally, the mixture is worked upin the same manner as Example 1 to give microcapsules.

EXAMPLE 12

In 2.5 ml of 20% aqueous gelatin solution (liquified by warming) isdissolved 500 mg of morphine hydrochloride and the solution is added to10 ml of a 20% dichloromethane solution of polylactic acid (average mol.wt. 15000). Thereafter, the same procedure as Example 1 is followed togive prolonged release microcapsules for injection.

EXAMPLE 13

In 2.5 ml of 20% aqueous gelatin solution (liquified by warming) isdissolved 150 mg of sodium diclofenac and the solution is added to 10 mlof a 20% dichloromethane solution of polylactic acid (average mol. wt.15000). The mixture is worked up in the same manner as Example 1 to givemicrocapsules for injection.

EXAMPLE 14

In 2.5 ml of a 20% aqueous gelatin solution (liquified by warming) isdissolved 1 g of methylephedrine hydrochloride and the solution is addedto 10 ml of a 20% dichloromethane solution of polylactic acid (averagemol. wt. 50000). The mixture is worked up in the same manner as Example1 to give methylephedrine microcapsules for injection.

EXAMPLE 15

In 3.0 ml of 20% aqueous gelatin solution (liquified by warming) isdissolved 1 g of chlorpromazine hydrochloride, and the solution is addedto 10 ml of a 20% dichloromethane solution of lactic acid-glycolic acidcopolymer (88.7/11.3; average mol. wt. 19000). The mixture is worked upin the same manner as Example 1 to give chlorpromazine hydrochloridemicrocapsules for injection.

EXAMPLE 16

In 3.0 ml of 30% gelatin (dissolved by warming) is dissolved 50 mg ofpridinol methanesulfonate and the solution is added to 10 ml of a 30%dichloromethane solution of lactic acid-glycolic acid copolymer(78.1/21.9, average mol. wt. 10000). The mixture is then worked up inthe same manner as Example 1 to give pridinol methanesulfonatemicrocapsules for injection.

EXAMPLE 17

Using 600 mg of chlordiazepoxide hydrochloride, the procedure of Example11 is followed to give microcapsules.

EXAMPLE 18

Using 800 mg of metoclopramide, the procedure of Example 12 is followedto give metoclopramide microcapsules for injection.

EXAMPLE 19

Using 1 g of imipramine, the procedure of Example 15 is followed to giveimipramine microcapsules for injection.

EXAMPLE 20

Using 750 mg of diphenhydramine hydrochloride, the procedure of Example14 is followed to give diphenhydramine hydrochloride microcapsules forinjection.

EXAMPLE 21

Using 750 mg of etilefrin hydrochloride, the procedure of Example 15 isfollowed to give etilefrin hydrochloride microcapsules for injection.

EXAMPLE 22

Using 300 mg of propranolol hydrochloride, the procedure of Example 14is followed to give propranolol hydrochloride microcapsules forinjection.

EXAMPLE 23

Using 250 mg of oxyfedrine hydrochloride, the procedure of Example 12 isfollowed to give oxyfedrine hydrochloride microcapsules for injection.

EXAMPLE 24

Using 300 mg of pentolinium, the procedure of Example is followed togive pentolonium microcapsules.

EXAMPLE 25

Using 1 g of phenformin hydrochloride, the procedure of Example 13 isfollowed to give phenformin hydrochloride microcapsules.

EXAMPLE 26

Using 2×10⁶ units of sodium heparin, the procedure of Example 15 isfollowed to give sodium heparin microcapsules.

EXAMPLE 27

Using 400 mg of adrenochrome monoaminoguanidine methanesulfonate, theprocedure of Example 12 is followed to give adrenochromemonoaminoguanidine methanesulfonate microcapsules for injection.

EXAMPLE 28

Using 800 mg of isoniazid, the procedure of Example 16 is followed togive isoniazid microcapsules for injection.

EXAMPLE 29

Using 750 mg of prednisolone sodium phosphate, the procedure of Example15 is followed to give prednisolone sodium phosphate microcapsules forinjection.

EXAMPLE 30

Using 100 mg of levallorphan tartrate, the procedure of Example 16 isfollowed to give levallorphan tartrate microcapsules for injection.

EXAMPLE 31

To 160 g (1.5 mol) of 80% lactic acid aqueous solution is added 38 g(0.5 mol) of glycolic acid, and the mixture is subjected to heatingunder reduced pressure in nitrogen gas stream at 100 to 150° C./350 to30 mmHg stepwise for 6 hours with removing distilled water, and then theresultant is subjected to condensation reaction at 175° C./6 to 5 mmHgfor for 36 hours to give lactic acid-glycolic acid copolymer (monomerratio: 75/25, average molecular weight 14000).

In 10 ml of dichloromethane and 3 ml of n-pentane is dissolved 2 g ofsaid lactic acid-glycolic acid copolymer which is synthesized withoutcatalyst.

To this solution is added 2.5 ml of 20% aqueous gelatin solutioncontaining 200 mg of TAP-144 which has been previously liquified bywarming at about 60° C., and the mixture is ultrasonicated (100W, a fewminutes), the given microfine W/O emulsion is immediately cooled down atabout 15° C. to cause gelation of the gelatin. This is then added to1000 ml of 0.5% polyvinyl alcohol in distilled water solution anddispersed using a homogenizer having a punching metal of 80 μm pores for60 seconds at 3000 r.p.m. to give a W/O/W emulsion. The emulsion isquickly transferred to a vessel in which the dichloromethane andn-pentane are desorbed under mixing with propeller mixer for 2 hours.The emulsion is then filtered through milipore filter with 8 μm poresand washed 5 times with 100 ml of distilled water.

Thereafter the procedure of Example 1 is followed to give TAP-144microcapsules for injection.

What we claim is:
 1. A method for producing a prolonged releasemicrocapsule for injection, which comprises redispersing a sphericalmicrocapsule having an average diameter of 2 to 200 μm, comprisingparticles containing a water-soluble drug, the particles being dispersedin a spherical microcapsule matrix composed of a polymer of lactic acidand glycolic acid having comonomer ratio within the range of about 100/0to 50/50and an average molecular weight within the range of about 5,000to 200,000, in an excipient selected from the group consisting ofmannitol, sorbitol, lactose and glucose and then solidifying,wherein heresulting microcapsule upon reconstitution in a vehicle for injection,provides greater stability than if no redispersing step is performed,and wherein the water-soluble drug is (Pyr)Glu-His-Trp-ser-Tyr-D-Leu-Leu-Arg-Pro-NH-C₂ H₅.
 2. The method as claimedin claim 1, wherein the comonomer ratio is 75/25.
 3. A prolonged releasemicrocapsule for injection which is produced by the method of claim 1.